An automatic metering device and method for anaerobic fermentation gas based on pressure method

Abstract

The present invention provides an automatic metering device and method for anaerobic fermentation gas based on a pressure method, the device including a reactor, a temperature sensor, a pressure sensor, an adsorption device, a one-way valve and a data processing module. During the metering process, by setting the pressure threshold for the headspace gas metering of the reactor, when the pressure of the headspace gas reaches the preset pressure threshold, the system automatically controls the one-way valve to release the gas to restore the pressure of the headspace, measures the volume of the released gas, and allows the system to enter the next metering cycle; at the same time, through the compensation algorithm of the data processing module, the effects of water vapor, purge gas, tail gas and standardization on the metering are selectively compensated, thereby achieving continuous and accurate gas flow measurement. The present invention adopts a pressure method to achieve adjustable resolution, combines high-precision sensing, intelligent algorithms and automatic control strategies, and provides an efficient, flexible and highly adaptable gas metering solution that can adapt to multiple application scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of metering devices, and in particular to an automatic metering device and method for anaerobic fermentation gas based on a pressure method. Background Art

[0002] Anaerobic digestion is a widely used technology for treating organic waste, effectively converting agricultural, urban, and industrial waste into biogas. Biogas, primarily composed of CH₄ and CO₂, is a key source of waste resource utilization and renewable energy recovery. The biomethane potential (BMP) of organic matter is a key metric used in anaerobic digestion, evaluating the amount of methane gas produced per unit mass of organic fermentation material in an anaerobic environment. Ensuring accurate gas measurement results is crucial for evaluating BMP testing, optimizing anaerobic digestion processes, and improving energy recovery efficiency.

[0003] Traditional gas measurement methods rely primarily on gas chromatography or gas sensors to determine gas concentration. This requires manual gas collection and volume measurement to further calculate the total volume based on the concentration. However, this method not only fails to capture the degradation kinetics of methane production, but the manual measurement process is cumbersome, time-consuming, and subject to significant errors. Compared to manual measurement, the main advantage of automated measurement technology lies in its ability to provide higher measurement accuracy and continuity, ensuring data consistency and reliability. It also significantly reduces manual operation time, significantly improving work efficiency, and providing a more convenient and efficient tool for gas metering.

[0004] Currently, automated measurement methods based on pressure use a pressure sensor to measure the pressure before and after anaerobic fermentation while maintaining a constant volume. The resulting methane gas is calculated from the total pressure difference in the reactor. However, this method is limited by the reactor's volume and the maximum pressure it can withstand, and requires the volume of the reaction materials and headspace within the reactor. This results in increased errors in the measurement results, poor repeatability, and the inability to accurately measure the generated gas. Furthermore, continuous feeding reactions with high gas production are unsuitable.

[0005] Beaubien et al. (1988) published "Automated high-sensitivity gas metering system for biological processes" in Biotechnol Bioeng, disclosing a pressure-based gas metering device that continuously releases headspace gas. A three-way valve controls the connection between the reactor and the gas collection bottle, and between the gas collection bottle and the external environment. The connection time between the gas collection bottle and the external environment is fixed, and the gas volume is calculated by measuring the number of connections between the gas collection bottle and the external environment. However, this method is sensitive to daily changes in atmospheric pressure and temperature, making gas metering accuracy susceptible to changes in the external environment. Furthermore, the fixed connection time makes it difficult to maintain an anaerobic environment within the reactor, affecting the normal progress of the anaerobic fermentation reaction. Furthermore, the method fails to account for metering errors caused by water vapor, purge gas, and residual exhaust gas.

[0006] Invention patent CN102395864B discloses a device for measuring ultra-low gas flow. After the gas flows into the device, it enters the gas compartment and gradually accumulates. When the gas accumulates to a certain amount, the gas compartment is lifted to release the gas, and then returns to the initial state to continue collecting gas. The device has a simple structure and can achieve accurate flow measurement. However, the resolution of the device is fixed, and the amount of gas released each time is constant, which makes it difficult to adapt to a wider flow rate range. At the same time, the device has a metering interval. When the gas compartment has not fallen yet, there is a situation where the gas is released without being measured, which leads to metering errors. In addition, when the amount of gas is not enough to lift the gas compartment, it cannot be measured, which will also cause metering errors.

[0007] In summary, current gas metering devices and methods have shortcomings such as narrow application scope, large metering error, insufficient continuous measurement performance, and inability to effectively adjust resolution. Summary of the Invention

[0008] This application describes a pressure-based automatic anaerobic fermentation gas metering device and method for measuring the volume of gas produced by anaerobic fermentation. This device and method are not only suitable for measuring the volume of gas produced by various reactors and reaction materials, but also provide continuous measurement capabilities. An embedded compensation algorithm ensures accurate and precise measurement, thereby ensuring the reliability of the measurement results. By adjusting the pressure release threshold, variable gas metering resolution is achieved to accommodate a wider range of gas flow rates, meeting the gas production metering requirements of anaerobic digestion.

[0009] The automatic gas metering device of the present invention comprises:

[0010] At least one reactor with good mass transfer effect;

[0011] at least one temperature sensor for monitoring the temperature of the headspace within the reactor;

[0012] at least one pressure sensor for monitoring the pressure of the headspace within the reactor;

[0013] At least one one-way gas valve, used to gradually release the gas generated in the reactor to keep the gas pressure inside the reactor relatively stable;

[0014] at least one adsorption device for containing a gas adsorbent to adsorb acidic gas, wherein the adsorption process is based on an irreversible reaction;

[0015] At least one data processing module is used to receive data such as pressure and temperature of the headspace in the reactor, and control the opening and closing of the one-way gas valve according to the real-time pressure data. At the same time, the amount of gas released this time is calculated according to a specific compensation algorithm, and the accumulated gas volume is added to the cumulative gas volume change. At the same time, the recorded gas volume can be converted into a BMP value according to experimental needs and the data is recorded;

[0016] In which, the reactor consists of a reaction bottle and a sealed bottle cap. The sealed bottle cap can be provided with multiple pipeline interfaces and corresponding valve ports for replenishing substances into the reactor or setting other sensors (pH, gas components, etc.) or taking samples, etc. The temperature sensor and pressure sensor are arranged in the reactor, and the one-way air valve is connected to a pipeline interface of the sealed bottle cap. The adsorption device can be arranged inside or outside the mouth of the reaction bottle, and connected between the reaction bottle and the one-way air valve to ensure that gases such as carbon dioxide are fully adsorbed.

[0017] When the one-way air valve is kept closed, the entire device is in a sealed state.

[0018] The adsorption device can use alkaline substances to adsorb carbon dioxide gas generated by the reaction. The reaction process is:

[0019] When CO2 is small: CO2+2OH - →CO 2- 3+H2O,

[0020] When CO2 is in excess: CO2+OH - →HCO - 3.

[0021] This reaction is irreversible under the environmental conditions required for general anaerobic fermentation.

[0022] The present application discloses an automatic metering device and method for anaerobic fermentation gas based on a pressure method, wherein the metering method comprises the following steps:

[0023] Step 1: Before the reaction starts, load the reactants to be monitored into the reactor and check whether there is any leakage after the device is connected. If the device is well sealed, purge inert gas into it to create an anaerobic environment, start the device, and set the pressure threshold P. 阈值 , where P 阈值 The selected pressure sensor can accurately monitor the value within the pressure variation range, that is, the gas measurement resolution of the device. Preferably, before the reaction, the reactor and the reactants are placed in the reaction environment to stabilize the initial pressure and temperature;

[0024] Step 2: The one-way valve is closed, and the temperature sensor and pressure sensor monitor the temperature and pressure of the headspace in the reactor and record them as the initial temperature T R0 and initial pressure P R0 ;

[0025] Step 3, as the anaerobic fermentation proceeds, the substrate in the reactor is gradually decomposed and converted by microorganisms, producing biogas (mainly a mixture of CH4 and CO2) and accumulating, wherein the generated CO2 is fully adsorbed by the alkaline substance in the adsorption device, and the remaining CH4 volume is measured by the device of the present invention;

[0026] Step 4: Select and enable the required compensation algorithm; the compensation algorithm includes the following methods: purge gas overestimation compensation algorithm, reactor tail gas compensation algorithm.

[0027] The remaining CH4 volume measurement process in step 3 is as follows:

[0028] The temperature sensor and pressure sensor monitor the temperature and pressure of the headspace in the reactor to obtain the real-time temperature T R and real-time pressure P R and the pressure value at the beginning of each measurement Calculate the pressure change ΔP in the headspace of the reactor using the following formula:

[0029] ,

[0030] Where ΔP is the pressure change in the reactor, P R is the real-time pressure value of the headspace in the reactor, It is the initial pressure of the headspace in the reactor at the beginning of this measurement.

[0031] Gas volume measurement algorithm

[0032] When ΔP ≥ P 阈值 When the temperature and pressure in the reactor are measured at the time of the ith release, they are T Ri and P Ri, the one-way valve is opened to release the methane and other gases produced by the reaction to keep the pressure in the reactor relatively constant. According to the ideal gas equation, since the headspace volume is fixed, the change in the amount of substance Δn is calculated by monitoring the changes in the pressure and temperature of the headspace in the reactor. The formula is as follows:

[0033] ,

[0034] ,

[0035] Where P is pressure, V is volume, n is the amount of substance, R is the ideal gas constant, T is temperature, and Δn i is the change in the amount of the headspace gas in the reactor measured for the i-th time, V R is the volume of the headspace in the reactor, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, is the initial pressure of the headspace in the reactor at the beginning of this measurement, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, It is the initial temperature of the headspace in the reactor at the beginning of this measurement.

[0036] Calculate the amount of gas released for the i-th time at the current temperature according to the gas molar volume formula ΔV i , the formula is as follows,

[0037] ,

[0038] Where ΔV i is the amount of gas released for the i-th time, Δn i V is the change in the amount of material in the headspace of the reactor measured this time, m T is the time when this measurement ends Ri The molar volume of methane gas at the temperature, R is the ideal gas constant, V R is the volume of the headspace in the reactor, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, is the initial pressure of the headspace in the reactor at the beginning of this measurement, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, It is the initial temperature of the headspace in the reactor at the beginning of this measurement.

[0039] The specific process of each compensation algorithm is as follows:

[0040]

Standard Condition Conversion Compensation Algorithm

[0041] The volume of the measured gas is converted to the volume under standard conditions to ensure the consistency and comparability of different experimental data. The amount of gas released for the i-th time under standard conditions is calculated according to the gas molar volume formula. i , using the molar volume V of methane gas under standard conditions ms , the formula is as follows:

[0042] ,

[0043] In the formula, ΔV is i is the volume change of the gas in the headspace of the reactor measured for the i-th time under standard conditions, ΔV i is the amount of gas released for the i-th time, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, P 标 is the pressure under standard conditions, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, T 标 The temperature is the standard condition.

[0044]

Water vapor correction compensation algorithm

[0045] Considering that the liquid in the reactor evaporates into water vapor, which is also measured by the device, this can cause metering errors and affect gas production. According to Dalton's law of partial pressure and Amagat's law of partial volume, the volume fraction of water is equivalent to the pressure fraction obtained by dividing the water vapor pressure by the total pressure. Therefore, the dry gas content can be calculated by subtracting the water content from the wet gas content.

[0046] The dry gas content f in the gas volume measured for the i-th time Di Calculated according to the formula:

[0047] ,

[0048] Where, f Di is the dry gas content in the gas volume measured for the i-th time, V vapi is the volume of water vapor in the gas volume measured for the i-th time, V gasi is the gas volume measured for the i-th time, P vapi is the pressure of water vapor in the gas volume measured for the i-th time, P gasi is the pressure of the gas measured for the i-th time,

[0049] Among them, the pressure of water vapor in the gas volume measured for the i-th time is P vapi It can be calculated according to the Antoine equation, the formula is as follows:

[0050] ,

[0051] Where, P vapi is the pressure of water vapor in the i-th measured gas volume, T i is the temperature at the time of the i-th measurement, A, B, C are Antoine constants,

[0052] Therefore, the volume change of dry gas in the gas volume measured for the i-th time is ΔV Di , the formula is as follows:

[0053] ,

[0054] Where ΔV Di is the volume change of dry gas in the gas volume measured for the i-th time, ΔV i is the amount of gas released for the i-th time, f Di is the dry gas content in the gas volume measured for the i-th time.

[0055]

Purge gas overestimation compensation algorithm

[0056] In order to ensure the normal progress of anaerobic fermentation, it is necessary to purge inert gas into the reactor before the reaction starts to create an anaerobic environment. However, the purge gas will fill the reactor headspace, affecting the subsequent measurement of the metering gas production. The residual ratio of the headspace purge gas at the i-th measurement is f Ni , the formula is as follows,

[0057] ,

[0058] Where, f Ni is the residual ratio of the headspace purge gas at the i-th measurement, ΔV i is the amount of gas released for the i-th time, V R is the volume of the headspace in the reactor.

[0059] Based on the headspace purge gas residual ratio and the reactor headspace gas volume during two adjacent measurements, the amount of methane gas in the gas volume measured at the i-th time, ΔV, is calculated. Ci , the formula is as follows,

[0060] ,

[0061] Where ΔV Ci is the amount of methane gas in the gas volume measured for the i-th time, ΔV i is the amount of gas released for the i-th time, V R is the volume of the headspace in the reactor, f Ni is the residual ratio of the headspace purge gas at the i-th measurement, f N(i-1) is the residual ratio of the headspace purge gas during the i-1th measurement.

[0062]

Gas change accumulation algorithm

[0063] Record the amount of gas released for the i-th time ΔV i , and added to the cumulative gas volume V generated in the previous i reactions ai , the formula is as follows:

[0064] ,

[0065] Where V ai is the cumulative amount of gas generated in the previous i times, V a（i-1） is the cumulative amount of gas generated in the previous i-1 times, ΔV i is the amount of gas released for the i-th time,

[0066] When the headspace pressure in the reactor is stable, the one-way valve is closed, and the temperature at this time is recorded again by the temperature sensor and pressure sensor as the initial temperature for the next gas release. , the pressure is the initial pressure of the next gas release .

[0067] Repeat step 3 to record the next change in gas volume.

[0068] Reactor tail gas compensation algorithm

[0069] When the reaction is finished, the one-way valve remains closed and the amount of gas remaining in the reactor is calculated. The temperature sensor and pressure sensor monitor the temperature and pressure in the reactor as real-time temperature T R and real-time pressure P R According to the ideal gas equation, the change in the amount of gas remaining in the reactor is calculated by monitoring the changes in the headspace pressure and temperature in the reactor. R , the formula is as follows:

[0070] ,

[0071] Where Δn R V is the change in the amount of gas remaining in the reactor. R is the volume of the reactor headspace, R is the ideal gas constant, P R is the real-time pressure value in the reactor, P R0 is the initial pressure in the reactor, T R is the real-time temperature in the reactor, T R0 is the initial temperature in the reactor,

[0072] Calculate the amount of gas released for the i-th time at the current temperature according to the gas molar volume formula ΔV i , the formula is as follows,

[0073] ,

[0074] Where, ΔV R is the volume change of the remaining unmeasured gas in the reactor, Δn R V is the change in the amount of gas remaining in the reactor. m T is the measurement time of this time R The molar volume of methane gas at the given temperature.

[0075] The amount of change in volume of the remaining unmeasured gas in the reactor ΔV according to the activation of the compensation algorithm R Perform compensation calculation and record the change in volume of the remaining unmeasured gas in the reactor after compensation. .Will Accumulated to the previous i times of cumulative gas production V ai , the formula is as follows:

[0076] ,

[0077] Where V a_end is the final cumulative gas volume of the reaction, V ai is the cumulative amount of gas produced in the previous i times, It is the volume change of the remaining unmeasured gas in the reactor after compensation.

[0078] The four compensation algorithms involved in steps 3 and 4 can be enabled or disabled by the user according to the specific situation. The optimal solution is to enable all of them, but one or more compensation algorithms can also be enabled at will.

[0079] After calculating the cumulative gas volume, if a BMP experiment is being conducted, the data processing module can also calculate the BMP value of the reactants based on the volatile solids (VS) content of the reactants. BMP is expressed as the volume of dry methane produced per kilogram of volatile solids (VS) converted to standard conditions (273.15 K and 101.33 kPa) in units of NmL / gVS.

[0080] The BMP experiment requires at least two groups of experiments (one group serves as a blank group to record the amount of methane produced by the residual VS in the inoculum, and the other group serves as an experimental group to record the amount of methane produced by the inoculum and the reactants). Each group of experiments is conducted in at least three parallel groups. Before the experiment begins, the VS of the inoculum and the reactants are measured and input into the data processing module.

[0081] The cumulative methane production in the experiment should be divided by the VS content added to the fermentation bottle. However, in the inoculum used in the fermentation bottle, there will be residual volatile solids that produce a certain amount of methane during anaerobic biodegradation. Therefore, this part should be subtracted from the methane production of the inoculum mud from the total methane production, and then divided by the VS content of the reactants to obtain the accurate material methane production. The calculation formula is as follows:

[0082] ,

[0083] Where, BMP s is the real-time methane potential value of the reactants, V at is the cumulative amount of methane gas produced by the experimental group, V ab is the cumulative amount of methane gas produced by the blank group, m It is the amount of inoculum added to the experimental group, m Ib is the amount of inoculum added to the blank group, VS s is the VS content of the reactants, m s is the amount of reactant added to the experimental group.

[0084] Beneficial effects:

[0085] 1. Accurately measure the volume of gas generated during the reaction process. The present invention uses high-precision temperature sensor and pressure sensor technology to achieve real-time acquisition of the headspace gas pressure and temperature in the reactor. By integrating the standard condition conversion compensation algorithm, the water vapor correction compensation algorithm, the purge gas overestimation compensation algorithm and the reactor tail gas compensation algorithm, the gas volume measured during the reaction process can be dynamically corrected, thereby improving the precision and accuracy of gas measurement and ensuring the reliability of the data. At the same time, the user can choose whether to enable all four compensation algorithms according to actual conditions, or can arbitrarily enable one or more compensation algorithms to provide the user with a variety of measurement results.

[0086] 2. Achieve fully automatic and continuous monitoring of reaction gases. The present invention uses an automated control system to precisely control the opening and closing states of the one-way gas valve on the reactor, achieving precise control of gas release during the reaction, thereby enabling fully automatic and continuous monitoring of the gases generated during the reaction. The device maintains relative stability of the headspace pressure within the reactor, avoiding potential inhibition of the normal fermentation process by product accumulation and preventing safety hazards caused by increased pressure. It is also suitable for gas metering in complex processes such as continuous anaerobic fermentation.

[0087] 3. Adjustable gas metering resolution. While maintaining a constant reactor headspace volume, the pressure release threshold is adjusted to change the amount of gas released per measurement. This allows for variable gas metering resolution to accommodate a wider range of gas flow rates, thus meeting diverse gas metering requirements in different industrial scenarios and experimental needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 Structural diagram of an automatic anaerobic fermentation gas metering device based on a pressure method according to the present invention.

[0089] Figure 2 An algorithm flow chart of an automatic anaerobic fermentation gas metering method based on a pressure method of the present invention.

[0090] Figure 3 A comparison diagram of the automatic anaerobic fermentation gas metering method based on the pressure method of the present invention.

[0091] Figure 4 The cumulative BMP curve of the preferred embodiment 2 of the present invention.

[0092] Figure 5 Gas release in the early stage of the reaction of the preferred embodiment 2 of the present invention.

[0093] Figure 6 Gas release in the later stage of the reaction of the preferred embodiment 2 of the present invention.

[0094] 1 reactor, 2 temperature sensor, 3 pressure sensor, 4 one-way gas valve, 5 adsorption device, 6 data processing module. DETAILED DESCRIPTION

[0095] like Figure 1 As shown, an automatic anaerobic fermentation gas metering device based on a pressure method comprises at least one reactor 1; at least one temperature sensor 2; at least one pressure sensor 3; at least one one-way gas valve 4; at least one adsorption device 5;

[0096] At least one data processing module 6 is used to receive data such as the pressure and temperature of the headspace in the reactor 1 and control the on and off of the one-way gas valve 4 according to the real-time pressure data, calculate the amount of gas released this time, and add it to the change in the cumulative gas amount. According to experimental needs, the recorded gas amount can be converted into a BMP value and the data can be recorded; the temperature sensor 2, pressure sensor 3, and adsorption device 5 are arranged on the inner side of the top of the reactor 1, and the one-way gas valve 4 is outside the top of the reactor 1. The temperature sensor 2, pressure sensor 3, and one-way gas valve 4 are electrically connected to the data processing module 6.

[0097] according to Figure 2The described gas automatic metering algorithm process first confirms the activation of the four compensation algorithms before starting metering, and records the initial temperature and pressure of the reactor headspace.

[0098] During the metering process, the temperature and pressure of the reactor headspace at the start of the i-th metering and the temperature and pressure of the reactor headspace at the i-th release are recorded, and the volume of gas released at the current temperature and pressure is calculated based on these two sets of data. Then, the following judgments are made in sequence:

[0099] "Whether the purge gas overestimation compensation algorithm is enabled": If the purge gas overestimation compensation algorithm is enabled, the purge gas volume contained in the measured gas volume must be excluded and the calculated result is used as the measured gas volume;

[0100] "Is the water vapor correction compensation algorithm enabled?" If the water vapor correction compensation algorithm is enabled, the volume of water vapor contained in the measured gas volume must be excluded, and the calculated result is used as the measured gas volume;

[0101] "Is the standard condition conversion compensation algorithm enabled?" If the standard condition conversion compensation algorithm is enabled, the measured gas volume needs to be converted to the gas volume under standard conditions.

[0102] After the above compensation calculation is completed, the final result value is determined as the gas volume released for the i-th time, and is accumulated and added to the i-1-th cumulative gas volume to obtain the i-th cumulative gas volume.

[0103] Repeat the above measurement process until the reaction is completed.

[0104] When the reaction is completed, it is necessary to determine whether the reactor tail gas compensation algorithm is enabled. If the reactor tail gas compensation algorithm is enabled, the unmeasured gas volume in the reactor headspace needs to be calculated and added to the i-th cumulative gas volume to obtain the final cumulative gas volume. Otherwise, the i-th cumulative gas volume is recorded as the final cumulative gas volume.

[0105] [Example 1]

[0106] The device of the present invention is used to measure the cumulative methane production value. The measurement scheme is to not release the gas produced during the fermentation process (traditional pressure measurement method), and to obtain the cumulative methane production value of the substrate by measuring the pressure increase in the reactor.

[0107] Experimental setup:

[0108] When setting up the experiment, it is necessary to avoid excessive headspace pressure in the reactor by maintaining a large headspace volume or diluting the reaction substrate. A sufficiently large adsorption device should be used, equipped with sufficient alkaline material to adsorb the acidic gases generated during the reaction.

[0109] For example, the total volume of the reactor is 2 L, the working volume is 0.5 L, and the fermentation temperature is 37°C.

[0110] The measurement method includes the following steps:

[0111] (1) Before the reaction begins, place the inoculum, substrate, nutrient solution, and water into the reactor, place a sufficient amount of flaky NaOH in the adsorption device, and check if there is any leakage after the device is connected. If the device is well sealed, purge inert gas into it to create an anaerobic environment and start the device. Set the pressure threshold P 阈值 100 kPa. Select to enable water vapor correction compensation algorithm;

[0112] (2) The one-way valve is closed, and the temperature and pressure sensors monitor the temperature and pressure conditions in the reactor. The initial temperature T R0 , initial pressure P R0 Calculate the water vapor partial pressure P at this temperature vap ;

[0113] (3) Calculate the real-time pressure change of the headspace in the reactor , when ΔP ≥ P 阈值 When the one-way valve opens, the methane and other gases produced by the reaction are released to prevent safety problems caused by excessive pressure. Since only the water vapor correction compensation algorithm is enabled, the calculation formula for the cumulative amount of methane gas produced becomes:

[0114]

[0115] Where Δn is the change in the amount of gas in the reactor, V R is the volume of the reactor headspace, P R is the real-time pressure value in the reactor, P R0 is the initial pressure in the reactor, T R is the real-time temperature in the reactor, T R0 is the initial temperature in the reactor, V a is the cumulative amount of methane gas in the reactor, V m is the molar volume of methane gas in the current environment, f D is the content of dry gas, P vap is the pressure of water vapor in a measured volume of gas, and R is the ideal gas constant.

[0116] The device is used to measure the cumulative methane production of a certain reactant during anaerobic fermentation. The measurement strategy is high resolution without releasing gas (traditional pressure measurement method). Only the water vapor correction compensation algorithm is enabled during the measurement process. The final record is the cumulative methane gas volume V a .

[0117] [Example 2]

[0118] like Figure 3 As shown, compared with traditional gas measurement methods that mainly rely on gas chromatography or gas sensors to determine gas concentration, manual gas collection and volume measurement are required to further calculate the total volume based on the concentration; the material methane production potential testing method of the present invention is based on the pressure method. After carbon dioxide is adsorbed, four compensation algorithms are used to accurately measure the volume of methane produced according to the pressure and temperature values of the reactor headspace.

[0119] The device of the present invention is used to measure the BMP value of cellulose powder. The metering scheme is to release and meter a certain amount of gas immediately after the reaction produces the gas during the fermentation process, and finally accumulate the metered amounts to obtain the BMP value of the cellulose powder.

[0120] Preparation of fermentation materials:

[0121] The inoculum of this experiment was taken from an operating anaerobic reactor, the reactant of which was lignocellulosic biomass; the substrate was cellulose powder.

[0122] In the BMP experiment, the following reagents need to be prepared as auxiliary:

[0123] Required reagents include:

[0124] Acidic gas adsorbent: commercial grade sodium hydroxide (NaOH) flakes, or NaOH solution of a certain concentration;

[0125] To adjust the pH of the mixture (inoculum, substrate, water, and nutrient solution), use the following reagents: 1N hydrochloric acid (HCl) solution, or 1N sodium hydroxide (NaOH) solution, or powdered sodium bicarbonate (NaHCO3);

[0126] In addition, a certain amount of nutrient solution is required. The nutrient solution formula of nutrients and trace elements is as follows:

[0127] A: Dissolve 2.7 g anhydrous potassium dihydrogen phosphate (KH2PO4), 11.2 g disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O), and 5.3 g ammonium chloride (NH4Cl) in distilled water and bring to a 0.5 L volumetric flask.

[0128] B: Dissolve 0.75 g calcium chloride dihydrate (CaCl2·2H2O), 1.0 g magnesium chloride hexahydrate (MgCl2·6H2O), and 0.2 g iron (II) chloride tetrahydrate (FeCl2·4H2O) in distilled water and dilute to a 0.5 L volumetric flask.

[0129] C: 0.05 g manganese chloride tetrahydrate (MnCl2·4H2O), 0.005 g boric acid (H3BO3), 0.005 g zinc chloride (ZnCl2), 0.003 g copper (II) chloride (CuCl2), 0.001 g disodium molybdate dihydrate (Na2MoO4·2H2O), 0.1 g cobalt chloride hexahydrate (CoCl2·6H2O), 0.01 g nickel chloride hexahydrate (NiCl2·6H2O), 0.005 g disodium selenate (Na2SeO3). Dissolve the above reagents in distilled water and dilute to a 0.5 L volumetric flask.

[0130] The ratio was adjusted as required in the experiment.

[0131] Experimental setup:

[0132] The total volume of the reactor was 500 mL, the working volume was 400 mL, and the fermentation temperature was 37°C. Two parallel experimental groups were set up in this BMP experiment to test the background gas of the inoculum and the gas production of the substrate respectively:

[0133] Table 1 Material properties and experimental settings

[0134]

[0135] The measurement method includes the following steps:

[0136] (1) Before the reaction begins, place the inoculum, substrate, nutrient solution, and water into the reactor, place a sufficient amount of flaky NaOH in the adsorption device, and check if there is any leakage after the device is connected. If the device is well sealed, purge inert gas into it to create an anaerobic environment and start the device. Set the pressure threshold P 阈值 5 kPa. Select to enable the purge gas overestimation compensation algorithm, water vapor correction compensation algorithm, standard condition conversion compensation algorithm, and reactor tail gas compensation algorithm.

[0137] (2) The one-way gas valve is closed, and the temperature sensor and pressure sensor monitor the temperature inside the reactor and record it as the initial temperature T R0 The pressure in the reactor is recorded as the initial pressure P R0 It is 104.8kPa, and the water vapor partial pressure at this temperature is 6.25993kPa.

[0138] (3) Calculate the real-time pressure change of the headspace in the reactor , the headspace pressure change curve is as follows Figure 5 and Figure 6 As shown, when ΔP ≥ P 阈值When the one-way valve is opened, the methane and other gases produced by the reaction are released to keep the pressure in the reactor relatively constant. The amount of methane gas change in the reactor headspace is calculated, and ΔV is added to the cumulative methane gas volume Va. The one-way valve is closed, and the pressure in the reactor headspace is equal to the external environment. The pressure at this time is re-recorded by the pressure sensor as the initial pressure. , the temperature sensor re-records the temperature at this time as the initial temperature .

[0139] Calculate the amount of gas released for the i-th time at the current temperature according to the gas molar volume formula ΔV i , the formula is as follows,

[0140]

[0141] Where ΔV i is the change in the volume of the gas in the headspace of the reactor measured for the i-th time, Δn i V is the change in the amount of material in the headspace of the reactor measured this time, m T is the time when this measurement ends Ri The molar volume of methane gas at the temperature, R is the ideal gas constant, V R is the volume of the headspace in the reactor, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, is the initial pressure of the headspace in the reactor at the beginning of this measurement, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, It is the initial temperature of the headspace in the reactor at the beginning of this measurement.

[0142] Since the purge gas overestimation compensation algorithm is enabled, the amount of methane gas in the gas volume measured for the i-th time is calculated based on the headspace purge gas residual ratio and the reactor headspace gas volume during the two adjacent measurements. Ci , the formula is as follows,

[0143]

[0144] Where ΔV Ci is the amount of methane gas in the gas volume measured for the i-th time, ΔV i V is the change in the volume of the gas in the headspace of the reactor measured for the i-th time, R is the volume of the headspace in the reactor, f Ni is the residual ratio of the headspace purge gas at the i-th measurement, f N(i-1) is the residual ratio of the headspace purge gas during the i-1th measurement.

[0145] Since the water vapor correction compensation algorithm is enabled, according to the partial pressure law proposed by Dalton and the partial volume law proposed by Amagat, the volume change of the dry gas in the gas volume measured for the i-th time is ΔV Di , the formula is as follows,

[0146]

[0147] Where ΔV Di is the volume change of dry gas in the gas volume measured for the i-th time, ΔV i is the change in gas volume measured for the i-th time, f Di is the dry gas content in the gas volume measured for the i-th time, P vapi is the pressure of water vapor in the gas volume measured for the i-th time, P gasi is the pressure of the gas measured for the i-th time.

[0148] Since the standard condition conversion compensation algorithm is enabled, the amount of gas released under standard conditions is calculated according to the gas molar volume formula ΔV i , using the molar volume V of methane gas under standard conditions ms , the formula is as follows,

[0149]

[0150] In the formula, ΔV is i is the volume change of the gas in the headspace of the reactor measured for the i-th time under standard conditions, ΔV i is the change in the gas volume of the headspace in the reactor measured for the i-th time, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, P 标 is the pressure under standard conditions, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, T 标 The temperature is the standard condition.

[0151] Therefore, the cumulative change in the headspace gas volume ΔV in the i-th reactor after compensation is recorded. 补偿i , and added to the cumulative gas volume V generated in the previous i reactions ai The calculation formula becomes

[0152]

[0153] Where V ai is the cumulative amount of gas generated in the previous i times, V a（i-1） is the cumulative amount of gas generated in the previous i-1 times, ΔV 补偿i is the volume change of the dry purge gas released for the i-th time under standard conditions, ΔV iis the change in the volume of the headspace gas in the reactor during the i-th measurement, P 标 is the pressure under standard conditions, T 标 is the temperature under standard conditions, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, P vapi is the pressure of water vapor in the gas volume measured for the i-th time, V R is the volume of the headspace in the reactor.

[0154] Repeat step (3) to record the change in the amount of methane gas.

[0155] (4) When the reaction is finished, the one-way valve remains closed. If the reactor tail gas compensation algorithm is enabled, the amount of unmeasured methane gas remaining in the reactor is calculated. The temperature sensor and pressure sensor monitor the real-time temperature T in the reactor. R1 At 37°C and real-time pressure P R1 The volume of the remaining methane gas in the reactor headspace is 106.1 kPa. Calculate the volume of the remaining methane gas ΔV R 0.9665 mL, and added to the cumulative methane gas volume V a ,

[0156]

[0157] Where V a_end is the final cumulative amount of methane gas in the reaction, V ai is the cumulative methane gas volume measured last time, ΔV R is the volume change of methane gas in the reactor headspace.

[0158] (5) During the reaction, the BMP value can be calculated based on the real-time cumulative methane production of the blank group and the experimental group.

[0159]

[0160] Where, BMP s is the real-time methane potential value of the reactants, V at is the cumulative amount of methane gas produced by the experimental group, V ab is the cumulative amount of methane gas produced by the blank group, m It is the amount of inoculum added to the experimental group, m Ib is the amount of inoculum added to the blank group, VS s is the VS content of the reactants, m s is the amount of reactant added to the experimental group.

[0161] At the end of the reaction, the final cumulative methane gas volume of the experimental group was Vat The final cumulative methane gas volume V in the blank group was 893.9393 mL. ab The BMP value of cellulose powder is calculated as follows:

[0162]

[0163] Where V at is the final cumulative methane gas volume of the experimental group, V ab is the final cumulative gas change of the blank group, m It is the amount of inoculum added to the experimental group, m Ib is the amount of inoculum added to the blank group, VS s is the VS content of the reactants, m s is the amount of reactant added to the experimental group.

[0164] The device is used to monitor the BMP value of cellulose powder. The BMP change curve is as follows: Figure 4 As shown in the figure, the measurement strategy uses a small resolution to release the headspace gas multiple times. The standard condition conversion compensation algorithm, water vapor correction compensation algorithm and reactor tail gas compensation algorithm are enabled during the measurement process. Finally, the cumulative methane gas volume V of the reaction is recorded. a_end It is 893.9393NmL, and BMP is 361.7670NmL / gVS.

[0165] Table 2 Changes in methane production in the experimental group

[0166]

[0167] Table 3 Cumulative methane production and BMP changes

[0168]

[0169] [Example 3]

[0170] When different headspace volumes are used for testing at the commonly used temperature for anaerobic fermentation, the measurement resolution corresponding to different pressure thresholds is shown in the following table.

[0171] Table 4. Resolutions corresponding to different headspace volumes and pressure thresholds at common temperatures

[0172]

[0173] By analyzing these data, we can clearly see the changes in the metering resolution of the automatic gas metering device under different headspace volumes and pressure threshold conditions, further demonstrating the flexibility and high adaptability of the present invention in different application scenarios, and providing a strong basis for selecting appropriate parameters according to specific needs in practical applications.

Claims

1. A method for automatic measurement of anaerobic fermentation gas based on pressure method, characterized in that: The measuring method comprises the following steps: Step 1: Before the reaction starts, load the reactants to be monitored into the reactor and check whether there is any leakage after the device is connected. If the device is well sealed, purge inert gas into it to create an anaerobic environment, start the device, and set the pressure threshold P. 阈值 , where P 阈值 The selected pressure sensor can accurately monitor the value within the pressure variation range; Step 2: The data processing module controls the one-way valve to close, and the temperature sensor and pressure sensor monitor the temperature and pressure of the headspace in the reactor and record them as the initial temperature T R0 and initial pressure P R0 ; Step 3: As the anaerobic fermentation in the reactor continues, the substrate in the reactor is gradually decomposed and converted by microorganisms, generating biogas and accumulating it. The generated CO2 is fully adsorbed by the adsorption device, and the remaining CH4 volume is measured; Step 4, selecting and activating the required compensation algorithm; the compensation algorithm includes the following methods: purge gas overestimation compensation algorithm, reactor tail gas compensation algorithm; The purge gas overestimation compensation algorithm is as follows: in order to ensure the normal progress of anaerobic fermentation, inert gas needs to be purged into the reactor before the reaction starts to create an anaerobic environment; however, the purge gas will fill the reactor headspace, affecting the subsequent measurement of the metering gas production; the headspace purge gas residual ratio f at the i-th measurement Ni , the formula is as follows, , Where, f Ni is the residual ratio of the headspace purge gas at the i-th measurement, ΔV i is the amount of gas released for the i-th time, V R is the volume of the headspace in the reactor; Based on the headspace purge gas residual ratio and the reactor headspace gas volume during two adjacent measurements, the amount of methane gas in the gas volume measured at the i-th time, ΔV, is calculated. Ci , the formula is as follows, , Where ΔV Ci is the amount of methane gas in the gas volume measured for the i-th time, ΔV i is the amount of gas released for the i-th time, V R is the volume of the headspace in the reactor, f Ni is the residual ratio of the headspace purge gas at the i-th measurement; It also includes the gas change accumulation algorithm: Record the amount of gas released for the i-th time ΔV i , and added to the cumulative gas volume V generated in the previous i reactions ai , the formula is as follows: , Where V ai is the cumulative amount of gas generated in the previous i times, V a(i-1) is the cumulative amount of gas generated in the previous i-1 times, ΔV i is the amount of gas released for the i-th time. When the headspace pressure in the reactor is stable, the one-way valve is closed, and the temperature at this time is re-recorded by the temperature sensor and pressure sensor as the initial temperature of the next gas release. , the pressure is the initial pressure of the next gas release ; Repeat step 3 to record the next change in gas volume.

2. A method according to claim 1, characterized in that The temperature sensor and pressure sensor monitor the temperature and pressure of the headspace in the reactor to obtain the real-time temperature T R and real-time pressure P R and the pressure value at the beginning of each measurement Calculate the pressure change ΔP in the headspace of the reactor using the following formula: ， Where ΔP is the pressure change in the reactor, P R is the real-time pressure value of the headspace in the reactor, is the initial pressure of the headspace in the reactor at the beginning of this measurement; When ΔP ≥ P 阈值 When the temperature and pressure in the reactor are measured at the time of the ith release, they are T Ri and P Ri , the one-way valve is opened to release the gas produced by the reaction to maintain the stability of the pressure in the reactor. According to the ideal gas equation, since the headspace volume is fixed, the change in the amount of substance Δn is calculated by monitoring the changes in the pressure and temperature of the headspace in the reactor. The formula is as follows: ， ， Where P is pressure, V is volume, n is the amount of substance, R is the ideal gas constant, T is temperature, and Δn i is the change in the amount of the headspace gas in the reactor measured for the i-th time, V R is the volume of the headspace in the reactor, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, is the initial pressure of the headspace in the reactor at the beginning of this measurement, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, is the initial temperature of the headspace in the reactor at the beginning of this measurement; Calculate the amount of gas released for the i-th time at the current temperature according to the gas molar volume formula ΔV i , the formula is as follows, ， Where ΔV i is the amount of gas released for the i-th time, Δn i V is the change in the amount of material in the headspace of the reactor measured this time, m T is the time when this measurement ends R1 The molar volume of methane gas at the given temperature.

3. A method according to claim 2, characterized in that The standard condition conversion compensation algorithm is as follows: convert the volume of the measured gas to the volume under standard conditions to ensure the consistency and comparability of different experimental data; calculate the amount of gas released for the i-th time under standard conditions ΔV according to the gas molar volume formula i , using the molar volume V of methane gas under standard conditions ms , the formula is as follows: ， In the formula, ΔV is i is the volume change of the gas in the headspace of the reactor measured for the i-th time under standard conditions, ΔV i is the amount of gas released for the i-th time, P Ri is the real-time pressure value of the headspace in the reactor at the end of this measurement, P 标 is the pressure under standard conditions, T Ri is the real-time temperature of the headspace in the reactor at the end of this measurement, T 标 The temperature is the standard condition.

4. A method according to claim 2, characterized in that The water vapor correction compensation algorithm takes into account that the liquid in the reactor is evaporated into water vapor and is also measured by the device, resulting in measurement errors and affecting gas production. According to Dalton's law of partial pressures and Amager's law of partial volumes, the volume fraction of water is equivalent to the pressure fraction obtained by dividing the water vapor pressure by the total pressure. Therefore, the dry gas content is calculated by subtracting the water content from the wet gas content. The dry gas content f in the gas volume measured for the i-th time Di Calculated according to the formula: ， Where, f Di is the dry gas content in the gas volume measured for the i-th time, V vapi is the volume of water vapor in the gas volume measured for the i-th time, V gasi is the gas volume measured for the i-th time, P vapi is the pressure of water vapor in the gas volume measured for the i-th time, P gasi is the pressure of the gas measured for the i-th time, Among them, the pressure of water vapor in the gas volume measured for the i-th time is P vapi According to the Antoine equation, the formula is as follows: ， Where, P vapi is the pressure of water vapor in the i-th measured gas volume, T i is the temperature at the time of the i-th measurement, A, B, C are Antoine constants, Therefore, the volume change of dry gas in the gas volume measured for the i-th time is ΔV Di , the formula is as follows: ， Where, ΔV Di is the volume change of dry gas in the gas volume measured for the i-th time, ΔV i is the amount of gas released for the i-th time, f Di is the dry gas content in the gas volume measured for the i-th time.

5. A method according to claim 2, characterized in that The reactor tail gas compensation algorithm is as follows: when the reaction is finished, the one-way valve is kept closed and the amount of gas remaining in the reactor is calculated; the temperature sensor and the pressure sensor monitor the temperature and pressure in the reactor as real-time temperature T R and real-time pressure P R According to the ideal gas equation, the change in the amount of gas remaining in the reactor is calculated by monitoring the changes in the headspace pressure and temperature in the reactor. R , the formula is as follows: , Where Δn R V is the change in the amount of gas remaining in the reactor. R is the volume of the reactor headspace, R is the ideal gas constant, P R is the real-time pressure value in the reactor, P R0 is the initial pressure in the reactor, T R is the real-time temperature in the reactor, T R0 is the initial temperature in the reactor, Calculate the amount of gas released for the i-th time at the current temperature according to the gas molar volume formula ΔV i , the formula is as follows, , Where ΔV R is the volume change of the remaining unmeasured gas in the reactor, Δn R V is the change in the amount of gas remaining in the reactor. m T is the measurement time of this time R The molar volume of methane gas at the temperature; The amount of change in volume of the remaining unmeasured gas in the reactor ΔV according to the activation of the compensation algorithm R Perform compensation calculation and record the change in volume of the remaining unmeasured gas in the reactor after compensation. ,Will Accumulated to the previous i times of cumulative gas production V ai , the formula is as follows: ， Where V a_end is the final cumulative gas volume of the reaction, V ai is the cumulative amount of gas produced in the previous i times, It is the volume change of the remaining unmeasured gas in the reactor after compensation.

6. An automatic anaerobic fermentation gas metering device based on a pressure method using the method according to any one of claims 1 to 5, characterized in that: include: at least one reactor; at least one temperature sensor; at least one pressure sensor; At least one one-way gas valve; at least one adsorption device; At least one data processing module, configured to receive pressure and temperature data of the headspace in the reactor and control the opening and closing of the one-way gas valve according to the real-time pressure data; The temperature sensor, pressure sensor, and adsorption device are arranged on the inner side of the top of the reactor, and the one-way gas valve is arranged on the outer side of the top of the reactor. The temperature sensor, pressure sensor, and one-way gas valve are electrically connected to the data processing module.

7. A metering device according to claim 6, characterized in that The one-way gas valve is used to release the gas generated in the reactor in sequence to keep the gas pressure inside the reactor stable; when the one-way gas valve is kept closed, the entire device is in a closed state.

8. A metering device according to claim 6, characterized in that The reactor consists of a reaction bottle and a sealed bottle cap, and the sealed bottle cap is provided with multiple pipeline interfaces and corresponding valve ports for replenishing substances into the reactor or setting other sensors or taking samples; the one-way air valve is connected to a pipeline interface of the sealed bottle cap, and the adsorption device is arranged inside or outside the bottle mouth of the reaction bottle, and is connected between the reaction bottle and the one-way air valve to ensure that the gas to be adsorbed is fully adsorbed.

9. A metering device according to claim 6, characterized in that The adsorption device uses alkaline substances to adsorb the carbon dioxide gas generated by the reaction. The reaction process is: When CO2 is small: CO2+2OH - →CO 2- 3+H2O, When CO2 is in excess: CO2+OH - →HCO - 3.

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